The invention relates to a safety valve adapted to respond to overheating of the external athmosphere surrounding said valve, e.g. in case of fire. The possible responses include the opening of said valve, e.g. when a valve intended for liquids is connected to an instrument for sprinkling the seat of a fire, as well as the closing of the valve, e.g. when the valve is a combustion gas valve fitted in the entrance pipe of a building.
Such valve will, in general terms, comprise a housing, e.g. tube-shaped, separating an internal passageway from an external athmosphere outside the housing, and also comprises an obturation body movable between an open position and an obturating position (i.e. a position in which said passageway is kept open, respectively closed by said obturation body), and further also comprises a control mechanism for said obturation body. The said body may have the form of a piston which is slidable inside a cylinder having one or more openings in the wall which are obturated or not by the piston in accordance with the position of the latter. It also may have the form of a ball or flap conforming to the valve seat in order to close the passageway when pushed against the valve-seat, or it may have any other form.
In such a valve, the position of the obturation body will be directed by a control mechanism which is based on a shape memory element, i.e. a mechanism by which the opening and/or closing movement is triggered by a signal delivered by a shape memory alloy element. This mechanism comprises one or more mechanical, fluidic, magnetic and/or electromagnetic elements, the function of which is to produce the movement of the obturation body when triggered by the shape-memory alloy element. Such an alloy, as well known, can, if properly prepared, exhibit different shapes in the warm and cold states, and provides the advantage that it produces sufficient energy to move the movable parts of the temperature command or control systems. This permits a simplification of these systems and avoids, if necessary, the use of electric components. For the abovementioned heat responsive valves, several control mechanisms can be conceived, depending upon whether the valve is to open or close in overheating conditions, whether it is permitted to open or to close again after the overheating conditions have ceased to exist, whether it shall open or close in the same or in the opposite sense as the pressure of the fluid, whether the shape memory alloy works as an element which pushes the obturation body into movement, or as a bolt element which temporarily prevents the movement of the obturation body which movement is then induced by another mechanical element, etc. In its simplest embodiment, the control mechanism may consist of only the shape memory alloy element which provides the function of a heat sensitive element, together with the function of producing the movement of the obturation body.